High acceleration shock testing air gun



Jan. 9, 1951 c. A. SHREEVE, JR., ET Al. 2,537,096

HIGH ACCELERTON SHOCK TESTING AIR GUN 3 Sheets-Sheet 1 g .w IJL .m\ S

Filed Feb. 4, 1949 mK W r. m .J 0. W W v uw d 6.. M W w n u m .m m .h 1Mf I m 5 5 A mh. Q A. H H. Nb. NV |l\ J. J. wd ov n. N* V /kv h. mh. my Y.Wk .m1/mw 4 Q Q mK v om Q Jan. 9,l 1951 C. A. SHREEVE, JR., ET AL.

HIGH ACCELERATION SHOCK TESTING AIR GUN 5 Sheets-Sheet 2 Filed Feb. 4,1949 J. H. Arms/rang @brom/m Jan. 9, 1951 C. A. SHREEVE, JR., ET-AL HIGHACCELERATION SHOCK TESTING AIR GUN y 3 Sheets-Sheet 5 Filed Feb. 4, 1949GAQShreez/e, ./r .l F ish/rin md 7 m m www V 3 l R Q 1 l n mm m..@m4/MM! a. III! RMN H WWHI E, mwmlmw MN ii|\lz4|| llllll wm S wm mw mw wvw J H. Armsfrong Patented Jan. 9, 1951 v 2,537,096 HIGH AooELERATIoN`snoon"rEsTrNd am GUN Charles A. Shreeve, '.lr.,

H. Armstrong,

College` Park, .Md., John Washington, D. C., and Joseph Fishkill, PerthAmboy, N. J.

Application February 4, 1949, Serial N 0474,64?,

romanica under the ect of March a, 1883, as amended April so, 192s; 370o. of. 757') 10 Claims.

This invention relates generall-y to test apparatus and moreparticularly to a device of this character adapted to accelerate anddecelerate, under controlled hydraulic pressures, the object under testfor the purpose of determining the effect of 4shock thereon.

Heretofore, considerable `diiiiculty has been encountered in the testingof certain types of naval ordnance particularly Ythose intended for useunder conditions of high acceleration shock such, for example, asprojectile fuzes, ltorpedo controls and high altitude aircraft launchedmines, or the like. Frequently field testing of such apparatus resultsin either the loss of the equipment or such damage thereto as torenderit valueless as a source of information.

lFor several ,years the Government has been interested in thedevelopment of equipment and the perfection of techniques whereby asmany as possible of these tests maybe conducted in the laboratory ratherthan in the field. Service evaluation wherein the completed 'Weapons aresubjected to performance tests duplicating the conditions of actual usemust, of course, be the nal step in development, but in the preliminarystages the advantages of controlled laboratory shock simulation hasVproven invaluable.

It has been frequently ndemonstrated both experimenta'lly andanalytically that -laboratory vapparatus 'for duplicating -l'le'ld shockconditions does not necessarily have to simulate exactly the extremeshock parameters "of each particular case, for example, short impulsivevelocity changes are known to produce the same response in a system ofrelatively -low natural frequency as that resulting thereto from 'loweraccelera-tion, longer duration pulses of equal total energy. Byproviding a test instrument, as in the case of the present invention,wherein the acceleration of the object under test may be accuratelycontrolled for producing the exact shock curve -desired, lends to a farwider range of laboratory shock application than permissible withinstruments `of the type heretofore devised.

According to the shock testing apparatus of the present invention, atest device in the form of an air gun is provided wherein a pistoncarrying the part to be tested initially is restrained from movementwithin the barrel of the gun by means of a frangible diaphragm until thepressure of a volume of air behind the piston and diaphragm has beenincreased to a predetermined value whereupon the diaphragm is rupturedand the piston is accelerated down the barrel by the pressure of thereleased air thereon to thereafter be brought toa gradual Vstop bycompression of the air in the barrel ahead of the piston. Byincreasingor reducing the air density in the air Volume before thepiston, the travel of ther piston'may be increased or reduced, as lthecase may be, lto cause the `shock pattern produced'thereby'to yconformto that desired. A pressure relief chamber and valve in the connectiontherewith providesa reservoir for storing a portion lof the kineticenergy in the air `ahead of the piston to thereby `substantially reduceoscillation of the Apiston at the Aend of the piston stroke.

IIt is-an object of the Apresent 'invention to provide a shock testingdevice adapted to accelerate and decelerate an object under test 'todetermine the'eiecto'f shockthereon.

Another object of the present invention 'is to provide new and improvedshock testing apparatus which may Abe voperated under controlledconditions to accelerate an object to be tested in a manner to impartshock eifectsthereto simulating vthe lshock veiec'ts received bytheobjects under actual conditions of service.

A further `object is 'to 'provide new and improved apparatus forsubjecting ordnance devices to shock effects which simulate the effectsof `shock received thereby under conditions of transport and service.

A still 'further object is `to provide a shock testing device of thischaracter adapted for testing a. `wide variety of Yordnance devices 'byapplying thereto a wide range of shock parameters encountered in theservice use of such devices.

A11-additional object is to provide a shock testing device of an air guntype wherein a pston carrying the part to be tested is acceleratedwithin jthe barrel of the gun by air pressure applied thereto anddecelerated by air compressed in the barrel `by movement of the pistontherein.

Other objects and many of 'the attendant advantages of this inventionwill be read'ly appreciated as the same becomes better understood byreference `to `the following detailed description when considered inconnection with the accompanying drawings wherein:

Fig. l is a side view in elevation of the air gun according to 'thepreferred form of the invention;

Fig. 2 is a somewhat `enlarged fragmentary sectional View taken throughthe breech assembly of the air gun and showing the arrangement of thepiston or projectile in the barrel thereof prior 4to acceleration.;

Fig. 3 is a lsomewhat enlarged detailed sectional View of the projectilewith the fuze under test mounted therein; and

Fig. 4 is a somewhat enlarged view partly in elevation and partly brokenaway of the muzzle tank or pressure relief chamber on the muzzle end ofthe barrel and the valve arrangement therebetween.

Referring now to the drawings and more particularly to Fig. 1 thereof,the test gun generally designated 5 is shown in operative associationwith respect to the control panel 6 therefor whereupon is arranged aplurality of valves andl gauges adapted to control and indicate,respectively, the various pneumatic pressures throughout the gun, aswill become more apparent as the description proceeds.

The high pressure portion 'I of the gun barrel generally designated 8,is shown as supported within a collar Q adapted to be secured, as bytrunnion clamps I2, to a carriage Il that may be of any suitable designsuch, for example, as that known as a Naval 5 inch gun mount Mk 15-1.

Secured to the high pressure section I3 of the barrel as by a boltedflange connection i3 is an extension I4 preferably formed from aseamless tubing having an internal diameter conforming exactly to thediameter of the bore of the high pressure barrel section 1 andpreferably ground and polished integrally therewith. The extension to becf a length satisfactory to permit suncient travel of piston I5, Fig. 2,carrying the part to be tested to apply to the part the shock conditiondesired.

Arranged over the muzzle end of the extension is a pressure tankgenerally designated I1 and comprised of an outer casing I8, Fig. 4, oneend of which is closed by an annular disk I9 secured as by welding at 23to the outer surface of the extension and thereafter secured to a flangeportion 2| of the casing as by bolts 22. The other end of the tank isshown as closed by a cap piece 23 fastened to flange 24 of the casing asby bolts 25. Cap piece 23 .preferably has Welded thereto a centralflange 29 for telescopically receiving and supporting the end ofextension I4 as at 34. A number of ribs 28 arranged radially orspiderlike about the outer surface of this cap and secured thereto as bywelding adds rigidity to the cap as well as provides a mounting surfacefor a handle ring 2S welded to the outer edge of the ribs and by whichthe cap may be lifted for mounting or removal from the tank opening. Aband or hoop 21 wielded to the periphery of fiange 24 supports the capwhile attaching bolts 25 are arranged therethrough. Ring gasketspreferably are employed as at 92 to make the pressure tank airtight.

Closing the end of the extension i4 is a check valve assembly generallydesignated 3E) including a cup-shaped valve plug or member 3l slidablyarranged within a counterbore 32 and adapted to be urged yieldably intobarrel closing position by pressure thereagainst of a helical springmember 33 arranged between the rear of the plug and the cover plate 23.Bore 32 is reduced at 93 thereby to form a seat for the valve member 3lat 94.

The valve member 3| is adapted to yield before the increasing airpressure within volume 35, as the piston is driven thereagainst by theforce of the greater air pressure within volume to allow a portion ofthe compressed air before the piston to flow through elongated ports 33or louvers into the tank volume 35 to be trapped therein by the closingof the valve as the pressure on opposite sides of valve member reaches anear state of equilibrium.

By referring to Fig. 2 of the drawings, the breech end of the highpressure barrel 1 may be seen as closed by a threaded block member 40that is provided with the usual pressure sealing elements, namely, amovable mushroom head 56 and gas check pad 51 having arranged thereinsteel sealing rings 58 and 59 adapted to expand outwardly with the padinto sealing engagement with the tapered surface 46 of the barrel liner43 as the mushroom head is pressed thereagainst by air pressure withinchamber or volume 31. Block 43 is adapted as it is rotated into breechclosing position within the threaded section 4I of the barrel to forceinwardly within the high pressure chamber 31, a spacer or volumecontrolled block 42 adapted, as it moves into the chamber, to pressforward upon the extending flange 43 of a frangible disc or diaphragmmember generally designated 44, Fig. 3, to grip the diaphragm betweenthe forward end of the spacer and a sealing ring member 41 that bearsagainst shoulder 43 of barrel liner 43. A pair Iof O ring gaskets 5U and5I conventionally arranged within suitable annular grooves providedtherefor in the sealing ring member 41 prevent escape of air by thesides of the ring from the high pressure chamber 31 into the barrelvolume or 4chamber 35.

By reason of the fact that the velocity of the projectile is controlledto some extent by the flow of air from chamber 31 as it expands behindthe piston, the volume control block 42 is provided with longitudinalslots or louvers 52 arranged through the wall section provided in thehollowed forward portion thereof, through which louvers air pressure maybe rapidly communicated to the base or back face of the piston from allthe air filled spaces within chamber 31 as the piston is acceleratedafter rupture of the retaining diaphragm 44 therefor.

The solid section or rear end portion of the spacer block 42 serves toreduce the air volume of chamber 31 thereby altering the resultantacceleration curve produced by the piston in proportion to the volume ofpropelling air under pressure. For producing varying shock conditions,blocks of varying displacement values may be used in substitutionselectively for the block 42.

The piston body 60, as best illustrated in Fig. 4, is generally 0fspool-shaped configuration and is provided with a bore 6I threaded at 62for receiving therein a projectile fuze 63 to be tested. It will beunderstood, however, that various other size fuzes or similar smallmechanisms may be secured to the piston for test by using suitableadapters equipped for threadedly connecting with the piston in themanner illustrated. Secured t0 the piston body on the forward end facethereof as by screws 65 is a bearing ring 55 formed from bronze orbrass, or the like, and operative to reduce the surface friction of theprojectile as it is accelerated down the bore.

Ehe piston retaining diaphragm 44 is clamped to the base or rear endface of the piston as by a flanged cap piece 61 drawn against thediaphragm by thc tightening of bolts 68 threadedly connecting with thepiston body. A spacer o1` washer 63 is arranged between the diaphragmand the piston body and is provided with a thickness selected inaccordance with the thickness of the particular diaphragm used whereby,as cap 61 is drawn tight upon the diaphragm by bolts 68.

afnemen the .sealing '.0 :ring te :carried ithefcaps iorced into sealingengagementwith the undercutsurface .1l .of `the piston vbody with .which.cap Bxl ,is adapted to `rnalse registering engagement therewith,thereby. prenentingpressure fromeleaking by the cap from Aaround the-bolts 16S therethrough. A .second ring 'i2 arranged .wit-hin ,a4suitable groove provided therefor .about the inner .surface of .the capflange '55 ,prevents the escape of `pressure between the .cap anddiaphragm. The piston assembly :is .adapted for being liiited `into athebarrel by the provision thereon of a flanged lug portion F3 `extending:rearward centrallyifromcthe cap ,piece and .suitable for connectingvwith :an elongated staff not shown, vwhereuponis provided a socket forgripping the .angeof the'lug.

Before operating the device, :a diaphragm` 6d suitable for theltestsselected .and may be formed from brass, aluminuinor plastic, as the'casemay be. The diaphragm must I'have Athe vrequirement for rupturing at thepressure necessary to produce the acceleration curvedesired. To providea diaphragm of slightly varying characteristics Without substitutingmaterials or altering the basic dimensions thereof, a groove varying indepth V:accordingly is machined in the face of the diaphragm at lli,thereby providing therein a weakened lsection whereupon the diaphragmwill break clean at the time `pressure is applied thereto of apredetermined value.

After the Adiaphragm has been secured to the piston and the part to betested suitably mounted thereon, the piston is lifted into the barreland clamped thereto in the manner heretofore described by the closing ofthe breech block 9. The valve 'i5 on the controlpanel 6 is then openedto permit air from compressors, not shown, to flow into the highpressure chamber V3l through the connection l@ to increase the pressuretherein to a value indicated upon the dial of `gauge Ti connectedto-cham'oer t? through the conduit TS.

As the pressure is increased Within the chamber to the yielding point ofthe diaphragm, the piston carrying the part under test is dischargeddown the barrel to attain peak acceleration almost instantaneously withthe piston gradually moving to a stop as the ai-r within volume 35 iscompressed before it. The valve 3l), operating in the manner heretoforedescribed, opens asthe pressure against it increases to trap Within tankli a percentage of the air and resulting energy therefrom, therebygreatly reducingoscillation o' the piston while the air pressure withinthe volumes or chambers '3? and 35 before. and after the piston reachesa state of equilibrium. To provide certain conditions of ytestparticularly `vfhere extreme high velocities are desired, air underpressure must be introduced through the connections 'lll and It2 intothe chambers 35 and 53S to apply an initial pressure to these volumes tothereby reduce the travel ofthe piston toconiorm to the length of thebarrel extension employed.

A choke ring El arranged in the muzzle as `indicated in Fig. 4 serves asa safety device to bind and stop further travel -of Ithe piston shouldthe h air before the piston not compress suiciently to stop the pistonas may be caused by a loose connection about thecap 23 or byescapementof air by the piston surfaces. As the piston is accelerated, the .recoilof the 'barrel is compensated by recoil cylinder 8l? connected tothebreach ring 18S as by rod E35, the barrel and extension assembly movingback'upon therollerequipped supports Si! and 9i thereof.

Arranged in spaced relation along the barrel 8 .is :a .pair of :drilledholes therein, inotfsh'own, through which light `.beams vare.directedito Astri-ke upon the element-.oi a pair lof .photeelectriccells arranged in containers :Sie and 95 respectively. As .theprojectile moves through thesbarrelzto successively interrupt theselight beams, a recording is made `on a chronograph :or like instrumentwhereupon the `exact zvelocity Aof .the projectile mayzbedetermined.

. "Upon completionzof the .testfand when the piston has come torestwithinthe barrel, the pressure .within volume .is :exhausted through theconnection .TF3 toall'ow thepiston .to begra'dually forcedbaclrward inthe `direeticm .of the .breech by the now greater pressureibefore thespiston within volume 35. -If 4'additional pressure is required Withinthis yvolume 'to force the 4piston to the breech-'end Lof the gun, -itmay be'suppli'ed .thereto fromlthe trapped gas -vvithinthe tank :llibyzmeans of Va suitable vlay-pass connection from port :32 Eto le or byair 4from thecompressors. The gauges 3.3, .85, 85, .and Athe panel arefconnected'respective'ly to the aforementionedconduits 16,118,l-9,.and.8*2 for indicating atiall times-the pressures within thevarious portions of the gun connected thereto.

'To iprovide Ymeans for determining :the f acceler tionof pistonfater'rupture of the retaining diaphragm therefor, suitable fluidconnections iidfmay .oe made with the Vvolume 35 Ia't-selectelilintervals along the `barrel inthe ypath of the-moving piston and adaptedas the lpiston lis accelerated `thereby to communicate pressure signalsto suitable recording apparatus Ylli-l' that may be mounted'beneathlthecontrol panel-S.

Gbviously'many modiiications and variations of the present invention are:possible inthe light of the above teachings. J t is th'ereforetobeunderstood that within the scope of the 'appended claims `the inventionmay be practiced otherwise thanas specica'llydescribed.

rIChe invention described herein may be manuiactured and used fby orlfor the Governmentv of the United lStates `oi America Yforlgovernmenta1 purposes without payment of any royaltiesthereonlor'thereior.

What is claimed as new and desired to be se cured by 'LettersPatentofthe United States is:

`1. A device for shock testing an object comprising, in combination, `anelongated barrel, closures for each rend of said barrel, a frangiblediaphragm secured to theinner Wall of saidbarrel for dividing the barrelinto two sealed compari',n ments, a piston adapted to carry the objectto be tested and held by saiddiaphragmin restrained position in thebarrel, -means for admitting -air under pressure into one of saidcompartments to increase the ypressure therein to a value equal to thefracture point of said diaphragm thereby releasing the piston `foraccelerated movement into the other of said compartments to increase thepressure therein to a value equal lto the pressure behind the piston.

'2. A shock inducing device of the character disclosed forapplyingacceleration shock to apparatus under test including, incombination, an elongated lbarrel, means for closing the ends of saidbarrel, a piston adapted -for carrying the apparatus to be tested andarranged insaid-barrel in predetermined spaced lrelation with respect toone .end thereof, a diaphragmvsecured to said piston and to said barrel"in pressure sealing relation therewith thereby to lform in the barrelltwo air volumes, means for admitting air under pressureY into *one vofthe said volumes for increasing the pressure therein to a value equal tothe fracture point of said diaphragm thereby releasing the piston foraccelerated movement into the second volume to be decelerated therein bythe compression of the air within the said second volume.

3. A device of the character disclosed adapted to apply accelerationshock to apparatus under test and including in combination, a mount, abarrel having a muzzle and breech end thereon arranged on said mount, ablock for closing the breech end of said barrel, a closely tting pistonadapted for carrying the apparatus to be tested and arranged for slidingmovement in said barrel, means including a frangible diaphragm forsecuring in sealing relation therewith the piston to said barrel inpredetermined adjacency to said block to form in the breech end of thebarrel a pressure chamber of a predetermined volume, means for admittingair under pressure into said pressure chamber for increasing thepressure therein to the fracture point of said diaphragm therebyreleasingsaid piston for accelerated movement through the barrel in thedirection of said muzzle, a valve seat provided in said muzzle, a valveplug, resiiient means for yieldably urging said valve plug in barrelclosing position in said seat, exhaust ports for said valve, a, pressurerelieving tank arranged over the muzzle end of said barrel and in Iiuidcommunication with said valve ports, said valve being adapted inresponse to the increase of air pressure in the muzzle portion of barrelcaused by the approach of the accelerated piston thereagainst to movesaid valve from said seat to thereby communicate a portion of thepressure in said muzzle to said tank, said valve being constructed tocut off air communication to the tank when the piston reaches the end ofsaid movement.

4. A shock testing device of the character disclosed adapted to applyacceleration shock to apparatus under test and including a mount, abarrel assembly yieldably supported on said mount, said barrel includinga breech chamber,

a breech block for closing the end of the barrel adjacent the breechchamber, a frangible diaphragm, means including a cylindrical spacerplug for clamping said diaphragm to the barrel upon closure of thebarrel by the block, means for admitting air under pressure into thebreech chamber for increasing the pressure therein to a value exceedingthe strength of said diaphragm, a piston adapted to receive theapparatus to be tested and clamped to said diaphragm, said piston beingoperative upon rupture of the diaphragm to accelerate in the barrel inresponse to the expanding air from the breech chamber, a check valveyieldably arranged in the end of said barrel opposite from said breech,and an exhaust port provided for said valve, said valve being adapted toopen and exhaust through said port a portion of the air compressed bythe approach of the piston thereagainst.

5. A device for shock testing an object comprising, in combination, anelongated barrel, a piston slideably supported within said barrel andconstructed and arranged to support said object slideably therein, meansincluding a frangible diaphragm arranged within one end of the barrel inpressure sealing and securing relation with respect to the piston so asto form therewith a pressure chamber in said one end of the barrel,means for admitting air under pressure into said pressure chamber, saiddiaphragm being so constructed as to be ruptured when the pressure ofthe air in the chamber reaches a predetermined value thereby to releasethe piston for accelerated movement toward the other end of the barrelby the pressure of the air thereon, means forming a pressure relievingchamber arranged at the other end of the barrel in air communicationtherewith, and valve means arranged in said other end of the barrel forcontrolling the flow of air from the barrel to said pressure relievingchamber, said valve means being constructed and arranged to cut off aircommunications between the barrel and said chamber when the pistonreaches the end of said movement.

6. A device for shock testing an object comprising, in combination, anelongated barrel closed at both ends, and object supporting pistonslidably mounted within said barrel and initially positioned in spacedrelation with respect to one end thereof, means including a frangiblediaphragm for releasably locking the piston in said initial position andin pressure sealing relation with respect to the barrel thereby to forma pressure chamber between the piston and said one end of the barrel,means for receiving air under pressure into said pressure chamber, saiddiaphragm being so constructed as to be ruptured when the air pressurein said chamber reaches a predetermined value thereby to release thepiston for accelerated movement toward the other end of the barrel, andmeans including a pressure relieving chamber at said other end of thebarrel for absorbing the kinetic energy stored in the compressed air infront of the accelerated piston thereby substantially to reduceoscillation thereof at the end of the piston stroke.

7. A device for shock testing objects comprising, in combination, amount, an elongated barrel yieldably arranged on said mount, meansincluding a removable member for closing one end of said barrel, aclosely fitted piston arranged in said barrel in predetermined spacerelation to said closed end thereof, said piston being constructed andarranged to support thereon the object under test, a frangible diaphragmsecured to the piston for releasably locking said piston in pressuresealing relation within said barrel thereby to form therein a pressurechamber between the piston and the closure therefor, a source ofcompressed air, means for admitting air under pressure from said sourceto said chamber, said diaphragm being so constructed as to be rupturedwhen the air pressure in said chamber reaches a predetermined valuethereby to release the piston for accelerated movement toward the otherend of the barrel, a normally closed pressure responsive valve arrangedat the other end of said barrel, a pressure tank disposed about saidbarrel and in fluid communication with said valve and adapted to receivetherethrough air compressed in the barrel by the accelerated piston,said valve being adapted to be opened by the pressure differentialthereagainst and to be closed and cut oi air communication between saidbarrel and tank when the piston reaches the end of said movement.

8. A device for shock testing an object including an elongated barrel,means including a check valve for closing one end of said barrel, abreech block for closing the other end of said barrel, a mushroom headmovably mounted on said block, a gas check pad arranged for compressioninto sealing engagement with the barrel as pressure is applied to saidhead, means forming a shoulder in the barrel in spaced adjacency to saidblock, means forming a sealing ring in abutment with said shoulder, agrooved annular flange member, a spacer member interposed between saidflange member and said breech block and adapted to compress the flangeinto pressure sealing engagement With the sealing ring upon closing ofsaid barrel by said block, a piston adapted for carrying the objectunder test constructed and arranged for clamping within said annularlange in peripheral alignment with said groove .therein and adapted tocooperate with said flange to divide said barrel into a high pressurechamber and a low pressure chamber, means including a conduit foradmitting air under pressure into said high pressure chamber to increasethe pressure therein to a value sufiicient to shear said iange at saidgroove thereby to release said piston for accelerated movement in thedirection of said valve to compress the air in said low pressure chamberto a value suicient to operate said valve to open position, a pressuretank in fluid circuit with said valve and adapted upon opening of thevalve to receive air under pressure from said low pressure chamber, saidvalve being adapted to operate to barrel closing position at the end ofsaid movement of the piston for reducing oscillatory motion of thepiston.

9. A device for applying acceleration shock to apparatus under testincluding in combination, a mount, an elongated barrel movably disposedon said mount, means for closing one end of said barrel including athreaded bloot: member, a normally closed pressure responsive valvedisposed Within said barrel and adapted to close the other end of saidbarrel, means forming a pressure seal between the barrel and blockincluding a mushroom head movably disposed within said block, a gascheck pad arranged between a portion oi said head and said block andadapted as pressure is applied to the head to compress into sealingadjacency with said barrel, means forming a shoulder in said barrel inspaced adjacency from said block, an annular frangible diaphragm, meanscooperating with said block for clamping said diaphragm to said shoulderin pressure sealing relation thereto, a piston adapted for carrying theapparatus to be tested secured within said diaphragm and cooperatingtherewith to form in said barrel a pressure chamber, means for admittingair under pressure to said chamber, said diaphragm being so constructedas to rupture when pressure of the air in the chamber reaches apredetermined value thereby to release the piston for acceleratedmovement with said apparatus carried thereon toward the valve closed endof said barrel in response to pressure of air thereon, a pressurerelieving tank arranged over said barrel and in air communication withsaid valve, said valve being adapted to open by the air compressed bythe accelerated piston thereby to vent said air to said tank, said valvebeing adapted to close the barrel as the piston reaches the end of saidmovement thereby to reduce oscillatory motion of the piston at the endof the piston stroke.

10. A device for shock testing an object comprising, in combination, anelongated barrel member, closures Tor sealing the ends of said barrelmember, a piston adapted for carrying the object under test arranged insaid barrel for sliding movement therein, means including a frangiblediaphragm secured in pressure sealing relation with said pisto-n and tosaid barrel in closely spaced adjacency to one end thereof formingwithin the barrel on opposite ends of said piston and diaphragm a rstpressure chamber disposed between the piston and diaphragm and said oneend of the barrel and a second pressure chamber respectively, means foradmitting air under pressure to said first pressure chamber to increasethe pressure therein to a value sufficient to rupture said diaphragmthereby to release said piston for accelerated movement in the directionof said second pressure chamber, said piston being adapted by saidmovement to compress the air in the second pressure chamber to a valuesuiiicient to arrest the movement of the piston as the piston approachesthe other end of the barrel.

CHARLES A. SHREEVE, JR. JOHN I-I. ARMSTRONG. JOSEPH FISHKIN.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 279,538 Chamberlain June 19, 1883556,058 Huey Mar. 10, 1896 2,356,992 Gilson Aug. 29, 1944

